Coils for horizontal field magnetic resonance imaging

ABSTRACT

Methods and apparatus for performing magnetic resonance imaging are disclosed. In one embodiment coil antennas for use with a horizontal field magnetic resonance imaging apparatus are placed in proximity to the scanning region to obtain magnetic resonance images. In accordance with another aspect of the invention the coil antennas are arranged so as to provide zero mutual inductance between the coils so as to increase the sensitivity of the measurement. Additional embodiments include quadrature coil antennas including two antennas, each having their vector fields substantially perpendicular to each other and to a static magnetic field. Methods for using the disclosed antennas in acquiring magnet resonance scans is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.10/266,070, filed on Oct. 7, 2002 and entitled “Coils For HorizontalField Magnetic Resonance Imaging” claims the benefit of and U.S.Provisional Application No. 60/327,329, filed on Oct. 5, 2001 andentitled “Coils For Horizontal Field Magnetic Resonance Imaging,” andU.S. Provisional Application No. 60/342,832, filed on Dec. 20, 2001, andentitled “MRI Apparatus Including Planar RF Coil Provided in a Seat,”the disclosures of which are hereby incorporated in their entirety byreference herein.

BACKGROUND OF THE INVENTION

The present invention relates to magnetic resonance imaging apparatusand procedures. In magnetic resonance imaging, an object to be imagedas, for example, a body of a human subject, is exposed to a strong,substantially constant static magnetic field. Radio frequency excitationenergy is applied to the body, and this energy causes the spin vectorsof certain atomic nuclei within the body to rotate or “precess” aroundaxes parallel to the direction of the static magnetic field. Theprecessing atomic nuclei emit weak radio frequency signals during therelaxation process, referred to herein as magnetic resonance signals.Different tissues produce different signal characteristics. Furthermore,relaxation times are a major factor in determining signal strength. Inaddition, tissues having a high density of certain nuclei will producestronger signals than tissues with a low density of such nuclei.Relatively small gradients in the magnetic field are superimposed on thestatic magnetic field at various times during the process so thatmagnetic resonance signals from different portions of the patient's bodydiffer in phase and/or frequency. If the process is repeated numeroustimes using different combinations of gradients, the signals from thevarious repetitions together provide enough information to form a map ofsignal characteristics versus location within the body. Such a map canbe reconstructed by conventional techniques well known, in the magneticresonance imaging art, and can be displayed as a pictorial image of thetissues as known in the art.

The magnetic resonance imaging technique offers numerous advantages overother imaging techniques. MRI does not expose either the patient ormedical personnel to X-rays and offers important safety advantages.Also, magnetic resonance imaging can obtain images of soft tissues andother features within the body which are not readily visualized usingother imaging techniques. Accordingly, magnetic resonance imaging hasbeen widely adopted in the medical and allied arts.

Several factors impose significant physical constraints in thepositioning of patients and ancillary equipment in MRI imaging. Many MRImagnets use one or more solenoidal superconducting coils to provide thestatic magnetic field arranged so that the patient is disposed within asmall tube running through the center of the magnet. The magnet and tubetypically extend along a horizontal axis, so that the long axis orhead-to-toe axis of the patient's body must be in a horizontal positionduring the procedure. Moreover, equipment of this type provides aclaustrophobic environment for the patient. Iron core magnets have beenbuilt to provide a more open environment for the patient. These magnetstypically have a ferromagnetic frame with a pair of ferromagnetic polesdisposed one over the other along a vertical pole axis with a gapbetween them for receiving the patient. The frame includes ferromagneticflux return members such as plates or columns extending verticallyoutside of the patient-receiving gap. A magnetic field is provided bypermanent magnets or electromagnetic coils associated with the frame. Amagnet of this type can be designed to provide a more open environmentfor the patient. However, it is still generally required for the patientto lie with his or her long axis horizontal.

Recently, ferromagnetic frame magnets having horizontal pole axes havebeen developed. As disclosed, for example, in commonly assigned U.S.patent application Ser. No. 08/978,084, filed on Nov. 25, 1997, and U.S.Pat. No. 6,414,490, the disclosures of which are incorporated byreference herein, and in copending, commonly assigned U.S. patentapplication Ser. No. 09/718,946, filed on Nov. 22, 2000, the disclosureof which is also incorporated by reference herein, a magnet having polesspaced apart from one another along a horizontal axis provides ahorizontally oriented magnetic field within a patient-receiving gapbetween the poles. Such a magnet can be used with a patient positioningdevice including elevation and tilt mechanisms to provide extraordinaryversatility in patient positioning. For example, where the patientpositioning device includes a bed or similar device for supporting thepatient in a recumbent position, the bed can be tilted and/or elevatedso as to image the patient in essentially any position between a fullystanding position and a fully recumbent position, and can be elevated sothat essentially any portion of the patient's anatomy is disposed withinthe gap in an optimum position for imaging. As further disclosed in theaforesaid applications, the patient positioning device may includeadditional elements such as a platform projecting from the bed tosupport the patient when the bed is tilted towards a standingorientation. Still other patient supporting devices can be used in placeof a bed in a system of this type. For example, a seat may be used tosupport a patient in a sitting position. Thus, magnets of this typeprovide extraordinary versatility in imaging.

Another physical constraint on MRI imaging has been posed by therequirements for RF antennas to transmit the RF excitation energy and toreceive the magnetic resonance signals from the patient. The antennathat receives the signals is positioned near that portion of thepatient's body that is to be imaged so as to maximize thesignal-to-noise ratio and improve reception of the weak magneticresonance signals. The antenna that applies RF excitation energy can bepositioned in a similar location to maximize efficiency of the appliedRF energy. In some cases, the same antenna is used to apply RFexcitation energy and to receive the magnetic resonance signals atdifferent times during the process. However, it is often desirable toprovide two separate antennas for this purpose.

The antennas are typically formed as one or more loops of electricallyconductive material. Such a loop antenna must be positioned so that theconductor constituting the loop extends along an imaginary plane orsurface having a normal vector transverse to the direction of the staticmagnetic field. Stated another way, the antenna must be arranged totransmit or receive electromagnetic fields in a direction perpendicularto the direction of the static magnetic field if it is to interact withthe precessing atomic nuclei. This requirement has further limitedavailable antenna configurations and techniques. For example, in avertical-field magnet such as a ferromagnetic frame magnet having avertical pole axis, it is impossible to use a loop antenna with the loopdisposed generally in a horizontal plane below the body of a recumbentpatient. Such an antenna has a normal vector which is vertical and henceparallel to the direction of the static magnetic field. A loop antennawhich encircles the patient with its normal vector extendinghorizontally can be employed. Also, planar or saddle-shaped loopsextending in generally vertical planes or surfaces, and having normalvectors in the horizontal direction transverse to the long axis of thepatient can be positioned on opposite sides of the patient. However,these antenna configurations do not provide optimum signal-to-noiseratios in some procedures as, for example, in imaging the spine, head orpelvic region.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the present invention an apparatusfor magnetic resonance imaging is provided. The apparatus includes amagnet defining a patient-receiving space and having a static magneticfield with a field vector in a substantially horizontal direction. Theapparatus further includes a patient support having a support surfacefor a human body. The patient support is positioned within thepatient-receiving space and is pivotable about a horizontal pivot axis.A coil antenna arrangement is provided for receiving a signal from apatient disposed within the receiving space. The coil antenna includes asolenoidal coil antenna having a first coil vector and a second antennahaving a second coil vector. The first coil vector and the second coilvector are transverse to the static magnetic field vector. The staticmagnetic field vector is oriented substantially transverse to the longaxis of a patient disposed within the patient-receiving space.

In accordance with an embodiment of the present invention an apparatusfor magnetic resonance imaging is provided. The apparatus includes amagnet defining a patient-receiving space and having a static magneticfield with a field vector in a substantially horizontal direction. Theapparatus further includes a patient support having a support surfacefor a human body. The patient support is positioned within thepatient-receiving space and is pivotable about a horizontal pivot axis.A quadrature coil antenna arrangement for receiving a signal from apatient disposed within the receiving space is also provided. Thequadrature coil antenna includes a first antenna having a first coilvector and a saddle coil antenna having a second coil vector. The firstcoil vector and the second coil vector are transverse to the staticmagnetic field vector. The static magnetic field vector is orientedsubstantially transverse to the long axis of a patient disposed withinthe patient-receiving space.

A method for using an apparatus for magnetic resonance imaging includingthe following steps is provided. (1) providing a magnet defining apatient-receiving space and having a static magnetic field with a fieldvector in a substantially horizontal direction. (2) Providing aquadrature coil antenna arrangement for receiving a signal from apatient disposed within the receiving space. The quadrature coil antennaincluding a solenoidal coil antenna having a first coil vector and asaddle coil antenna having a second coil vector. The first coil vectorand the second coil vector is transverse to the static magnetic fieldvector. (3) Positioning a patient on a support wherein the patient bodyis supported and is positioned within the patient-receiving space and ispivotable about a horizontal pivot axis. Wherein the static magneticfield vector is oriented substantially transverse to the long axis of apatient disposed within the patient-receiving space. (4) Elicitingmagnetic resonance signals by transmitting RF energy to the body andreceiving the magnetic resonance signals. Wherein at least one of thetransmitting and receiving steps is performed at least in part by use ofthe solenoidal coil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustratively depicts a front view of an apparatus in accordancewith an embodiment of the present invention;

FIG. 2 is a side view of the apparatus of FIG. 1;

FIG. 3 illustratively depicts a top view of an antenna in accordancewith an aspect of the present invention;

FIG. 4 is an edge view of the antenna of FIG. 3;

FIG. 5 is a side view of the apparatus of FIG. 1 with the patientdepicted in a horizontal position;

FIG. 6 illustratively depicts a perspective view of first and secondantennas in accordance with an aspect of the present invention;

FIG. 6A illustratively depicts a perspective view of first and secondantennas in accordance with a further aspect of the present invention;

FIG. 7 schematically illustrates a saddle coil antenna in accordancewith another aspect of the present invention;

FIG. 8 illustratively depicts a patient support apparatus in accordancewith another aspect of the present invention;

FIG. 9 illustrates an embodiment of a quadrature coil antenna havingsolenoidal coil antenna and a planar coil antenna;

FIG. 9A illustrates another embodiment of a quadrature coil antennahaving solenoidal coil antenna and a planar coil antenna;

FIG. 10 illustrates another embodiment of a quadrature coil antennahaving a solenoidal coil antenna and a saddle coil antenna;

FIG. 11A illustrates a schematic of yet another embodiment of aquadrature coil antenna having a solenoidal coil antenna and a saddlecoil antenna;

FIG. 11B illustrates the quadrature coil antenna of FIG. 11A without theexternal casing so as to reveal the arrangement of the solenoidal andsaddle coil antennas; and

FIG. 12 schematically illustrates another embodiment of resonanceimaging magnet in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning to FIGS. 1 and 2, there is illustrated an apparatus 1 accordingto one embodiment of the present invention. The apparatus 1 includes astatic field magnet having a frame 10 including a pair of poles 12spaced apart from one another along a horizontal pole axis 14. Frame 10further includes flux conducting and return members that, in theparticular embodiment illustrated, include a pair of sidewalls 16 andcolumns 18 extending between the sidewalls 16. The particular framedepicted in FIGS. 1 and 2 is generally in accordance with theaforementioned U.S. patent application Ser. No. 09/718,946, (hereinafter“the '946 application”) although other configurations can be employed.The opposed poles define a patient-receiving space or gap 20 betweenthem. The magnet further includes a source of magnetic flux adapted todirect into and out of the gap through poles 12 so as to form a staticmagnetic field having a field vector B₀ in the horizontal direction,parallel to pole axis 14. In the particular embodiment illustrated, theflux source includes a pair of electromagnet coils 22 encircling poles12. These coils may be superconductive or resistive coils. Alternateflux sources such as coils disposed at other locations along theferromagnetic frame and permanent magnets also may be employed.

The apparatus further includes a patient support assembly including abed 24 defining an elongated patient supporting surface 26 having alengthwise axis 25 and a platform 28 projecting from the supportingsurface at a foot end of the bed. In addition, a seat may be mounted tosupporting surface 26 to allow a patient to be positioned in a sittingposition. The patient supporting assembly further includes a frame 30.Bed 24 is pivotably mounted to the frame 30 for movement about agenerally horizontal pivot axis 32. Pivot axis 32 is substantiallyparallel to pole axis 14. Bed 24 can pivot between an upright positionin which the lengthwise direction over the bed extends generallyvertically as seen in FIG. 2 and a fully horizontal position shown inFIG. 5, in which the lengthwise direction of the bed 24 extendshorizontally. As further described in the '946 application, bed 24 alsomay be mounted for vertical motion relative to frame 30 and hencerelative to the static field magnet 10. Moreover, frame 30 can bemounted for horizontal movement relative to the static field magnet.Appropriate actuators and control devices (not shown) are provided formoving the bed and for moving support frame 30.

The patient support assembly further includes a first antennaschematically depicted as a planar box 34 in FIGS. 1, 2 and 5. As bestseen in FIGS. 3 and 4, the antenna includes a plurality of coils 36 eachincluding a winding extending in a loop. Each loop may be provided witha conventional coupling to a separate coaxial cable or other output line37 for conveying signals to a receiver or receiving signals from atransmitter. Also, each loop may include a capacitor (not shown) inseries and/or in parallel with the conductor forming the loop so as todefine a resonant antenna circuit. The windings of each coil extendalong a slightly curved coil surface seen in edge view in FIG. 4. Theterm “coil surface” as used herein refers to an imaginary surfacedefined by the central axis of the conductors constituting the coil orantenna. For example, in the special case of a flat circular coil, thecoil surface is the plane of the circle. Each coil surface defines acoil vector V_(c) normal to the coil surface itself. In the case of acurved coil surface, the coil vector of the coil surface as a whole canbe taken as the integral of the normal vector to the coil surface overthe entire area of the coil surface inside the coil.

The coils 36 are arrayed along the lengthwise axis 25 of bed 24 so thatthe coils overlap one another as shown in FIG. 3. Such a mutualoverlapping arrangement results in the coils having zero or nearly zeromutual inductance between the coils. Other arrangements which result innearly zero mutual inductance include arranging the coils in a planethat may extend along an elongated patient support. Coil surfaces 36extend generally parallel to the patient support surface 26 of bed 24.Thus, the normal vectors of the coil surfaces are transverse to thepatient support surface 26 of the bed. The coils may be formed on athin, plate or sheet that overlies surface 26. Alternatively, the coils36 may be mounted inside of the bed so that the coils are disposedbehind surface 26. Conventional padding or covering layers (not shown)may be provided over the coils and/or support surface 26 for patientcomfort.

The apparatus also includes, or is used in conjunction with,conventional field gradient coils (not shown) for applying magneticfield gradients within the patient-receiving space or gap 20 and an RFreceiver and transmitter (not shown) for applying RF signals through oneor more loops 36 of antenna 34 and for receiving magnetic resonancesignals using one or more loops 36. Additionally, the apparatus includesconventional control and reconstruction equipment for actuating thevarious elements discussed above including the gradient coils and RFtransmitter and receiver to elicit magnetic resonance signals and toconvert the resulting magnetic resonance signals into a set of datadefining an image of the patient. These elements may use theconventional techniques and principles of the magnetic resonance art andaccordingly are not discussed in detail herein.

In a method according to a further aspect of the invention, a patient Pis disposed on patient support 24 so that the patient's body overliesthe support and the first antenna 34. In the position illustrated, theposterior surface of the patient's torso is closely juxtaposed to thepatient support and with the first antenna so that the patient's spineis adjacent to the first antenna. The anterior-posterior axis of thepatient's body is parallel to the coil vector V_(c) of the first antennacoils. The coil vector V_(c) lies in a plane perpendicular to the poleaxis 14. Thus, regardless of whether it is in an upright position asseen in FIG. 2 or in a fully horizontal position as seen in FIG. 5, orat any angle between these positions, the coil vector V_(c) of the firstantenna is perpendicular to the static magnetic field B₀ so that thecoils of the first antenna can interact with the body tissue to excitethe nuclei to receive magnetic resonance signals. This arrangementprovides excellent signal-to-noise ratio. Any portion of the patient'sspine can be imaged using any one or more of the coils 36A-36D in thefirst antenna. Further, this arrangement is entirely non-claustrophobic.The patient need not be constrained by the coils of the first antenna atall and the patient need not even be aware of the presence of theantenna.

Stated another way, the patient support surface 26 of support 24 liessubstantially in a plane parallel to the pole axis 14 and hence parallelto the field vector of the static field magnet. This orientation allowsthe use of coils having coil surfaces generally parallel to the supportsurface. This arrangement of the support surface is different from therelative orientation of support surface and pole axis in a conventional“open” static field magnet having a vertical pole axis and a beddefining a substantially horizontal support surface, with the plane ofthe support surface perpendicular to the pole axis.

The same arrangement can be employed for imaging the patient in a proneposition or standing position with the anterior surface of the torsofacing the patient support surface 26. Also, this arrangement can beused with the patient in a sideways position, with his lateral axis(shoulder-to-shoulder axis), parallel to the coil vectors V_(c). Asimilar arrangement can be used for imaging portions of the body otherthan the torso as, for example, the head or legs.

Turning now to FIG. 6, there is shown a perspective view of first andsecond antennas in accordance with another embodiment of the presentinvention. As FIG. 6 shows, a generally solenoidal second antenna 150including a plurality of coils or loop windings 152 is used inconjunction with a first antenna 34 (similar to that discussed above).Each coil 152 of the second antenna extends in a plane transverse to theaxis 153 of the antenna, and thus defines a coil having a coil vectorV_(c152) extending substantially parallel to the axis 153 of thesolenoid and parallel to the coil vectors of the other coils. Thesolenoidal coils may be electrically coupled to one another usingcouplers (not shown) similar to those discussed above with reference toFIG. 3 or, preferably, may be electrically independent of one another.In any event, whether electrically coupled together or not, thesolenoidal coils magnetically behave as one solenoidal coil, i.e.,magnetic coupling is independent of electrical coupling. The firstantenna 34′ is similar to the first antenna 34 discussed above withreference to FIG. 3. The patient is positioned on the patient supportingsurface (not shown) so that the patient overlies the first antenna 34and so that the coils of the second antenna 150 encircle the patient'sbody. Solenoidal antennas that can be mounted so as to encircle the bodyof the patient in a convenient manner are disclosed, for example, inU.S. Pat. No. 4,887,038, the disclosure of which is hereby incorporatedby reference herein. In FIG. 6, the patient and the second antenna 150are depicted at a substantial distance above the first antenna 34′ forclarity of illustration. In practice, the patient's body is positionedas close as is practicable to the first antenna.

In this arrangement, the coil vectors V_(c152) of the second antenna aresubstantially perpendicular to the coil vectors V_(c34′) of the firstantenna and the coil vectors of both antennas are substantiallyperpendicular to the pole axis 14 and to the static field vector B₀, sothat signals may be transmitted and/or received by either or both thefirst and second antennas. For example, the RF signals used to excitethe nuclei may be transmitted by the second antenna and received by thefirst antenna or vice versa. Here again, the patient support may bearranged with the long axis of the patient's torso or other bodystructure horizontal or vertical.

Further in accordance with another aspect of the present invention, thefirst antenna 34′ of FIG. 6 is replaced with a planar antenna of thetype depicted in FIG. 6A. In particular, first antenna 44 includes oneor more planar coil antennas, illustratively depicted as coils 44 ₁through 44 ₃. Coils 44 ₁ through 44 ₃ each comprise one or more windingsextending in a loop. Each coil, 44 ₁ through 44 ₃, includes a coilsurface as described hereinabove. In addition, each coil surface definesa coil vector V_(C44) normal to the coil surface. Although coils 44 ₁through 44 ₃ do not overlap, as in the embodiment shown in FIGS. 3 and4, the use of a planar antenna of the type depicted in FIG. 6A for firstantenna 44 results in an improvement in the signal-to-noise ratio of upto √{square root over (2)}.

In a further embodiment, schematically illustrated in FIG. 7, the firstantenna is a saddle coil having a pair of windings each including a pairof axial runs A and a pair of arcuate runs R at the ends of the axialruns. Such a saddle coil defines a pair of coil surfaces in the form ofsectors of a cylindrical surface. The coil vector of such a coil isperpendicular to the axis of the cylindrical surface. The first antennamay be arranged so that one of the saddle windings is disposed adjacentto the patient supporting surface 26 whereas the other is disposedremote from the patient supporting surface so that the patient's body isdisposed between the two coils. Also, the first antenna may includeadditional sets of windings similar to the single set discussed above inreference to FIGS. 3 and 4. One set may be disposed adjacent the patientsupporting surface whereas the other set may be disposed remote from thepatient supporting surface, and the patient may be held between thesetwo sets. A solenoidal coil similar to coil 150 discussed above can beused in conjunction with such a first antenna.

In a further variant, the patient support may have a form other than anelongated bed. For example, as seen in FIG. 8, the patient supportincludes a chair having a seat 223 projecting in a forward or horizontalplane and a back 224 projecting upwardly from the seat so that the seatis disposed forward of the back. The back defines a first patientsupport surface 226 extending generally in a vertical plane whereas theseat defines a second patient support surface 227 extending generally ina horizontal plane. The seat is mounted in the patient-receiving spaceof a horizontal field magnet as discussed above. A first antenna 234extends in or on the back so that it is closely juxtaposed with thefirst support surface 226. The first antenna has one or more coils withcoil vectors V_(c234). A second antenna 235 extends in or on seat 223 sothat it is closely juxtaposed with the second support surface 227. Thesecond antenna 235 includes one or more coils with a coil vectorV_(c235). Both of these coil vectors are transverse to pole axis 214and, therefore, both antennas can interact with atomic nuclei in thesubject's body. The seat can be supported for pivoting motion and/or forvertical or horizontal movement within the patient-receiving space asdiscussed above. Even if the seat is pivoted about a horizontal axisparallel to the pole axis, the coil axes of both antennas will remainperpendicular to the pole axis. Apparatus according to this embodimentcan be used, for example, to image the spine of a patient in the seatedposition or to image the perineal region or to image other structures inthe patient's body. In particular, the apparatus of FIG. 8 may beadvantageously used to image the pelvic region of a patient, asdescribed in commonly assigned U.S. Application No. 60/342,382, filed onDec. 20, 2001, and commonly assigned non-provisional United Statesapplication of Damadian, et al., entitled “MRI Apparatus IncludingPlanar RF Coil Provided in a Seat,” filed on even date herewith, thedisclosures of which are hereby incorporated by reference herein.

Further in accordance with this aspect of the present invention, thequadrature coil arrangement of FIG. 8 may be achieved in an alternativeembodiment by using seat 223 in combination with a planar coil antenna.In particular, first antenna 234 may comprise a planar coil antennaenclosed in a box. The box may then be inserted between support surface226 and the surface of the patient adjacent to support surface 226,e.g., the patient's back. The second antenna 235 is positioned orarranged so that it is positioned adjacent to the second support surface227 or the sitting patient. Such a modular arrangement provides forgreater flexibility yet while allowing for better signal-to-noise ratio.

The seat and/or the back of a chair as described above with reference toFIG. 8 can be provided as a removable element which can be attached toan elongated, bed-like patient support of the type discussed withreference to FIG. 1. The first and second antennas likewise may be builtinto these removable elements, or may be provided as separate elements.Methods for attaching and adjusting the seat if implemented as aremovable element are disclosed in commonly assigned U.S. applicationSer. No. 10/131,843 (“the '843 application”), the disclosure of which ishereby incorporated by reference in its entirety.

Until now the arrangement shown in FIG. 8 was not considered exemplaryof a class of antenna or coil arrangements commonly referred to as“quadrature coils.” In such an arrangement the coil vectors associatedwith each of the antennas have mutually perpendicular axes. However, inaccordance with this aspect of the present invention, the arrangement oftwo planar coils as shown in FIG. 8 may be used in a quadrature coilarrangement. In particular, in FIG. 8 the coil vector V_(C234) ofantenna 234 is shown as projecting in a generally horizontal directionwhereas the coil vector V_(C235) of antenna 235 is shown as projectingin a generally vertical direction. In this way both coil vectors aretransverse to each other while being at the same time, as previouslynoted, transverse to the horizontal magnetic field B₀, which is orientedparallel to pole axis 214. As described hereinabove, other novelquadrature coil arrangements are achievable in accordance with thisaspect of the present invention. A quadrature coil antenna arrangementadvantageously improves the signal-to-noise ratio by a factor up to

$\sqrt{2}.$As a practical matter, the quadrature coil arrangement reduces themeasurement or MRI scanning time by approximately one-half. That is, ameasurement that takes approximately two minutes using a quadrature coilantenna arrangement will take approximately four minutes using anotherantenna arrangement. This improvement in performance translates intoincreased efficiency at MRI facilities.

The arrangement shown in FIG. 6 may also be used as a quadrature coilantenna arrangement. In particular, solenoidal or second antenna 150 hasa coil vector V_(C152) extending substantially parallel to the axis 153of the antenna 150. The coil vector V_(C34′) of the first antenna 34′ issubstantially perpendicular to the coil vector V_(C152) of the of thesecond antenna 150. The coil vectors of both the first and secondantennas, V_(C34′) and V_(C152), respectively, are also substantiallyperpendicular to the static field vector B₀. As such, the first andsecond antennas form a quadrature coil arrangement when used to receivethe magnetic resonance signals.

Turning now to FIG. 9, there is illustrated another embodiment of aquadrature coil arrangement. Quadrature coil antenna 300 includes afirst antenna schematically depicted as a planar box 302. The one ormore coils of the first antenna 302 may be arranged along a planarsurface as shown in FIG. 3 and as shown by broken lines 303 in FIG. 9.First antenna 302 defines a coil vector V_(C302) that projects in adirection substantially transverse to the planar surface and, whenattached to bed 24, transverse to the patient support surface 26 of thebed 24 (see FIGS. 1 and 2). Quadrature coil antenna 300 includes asecond antenna 312 having solenoidal coil portions 314, 316 and 318. Thecoil vector V_(C312) of the second magnet 312 projects in a directiontransverse to the first antenna coil vector V_(C302). Both the first andsecond coil vectors, V_(C302) and V_(C312), are perpendicular to staticfield vector B₀ of a horizontal field magnet of the type shown in FIGS.1 and 2. First antenna 302 augments the signal of the second antenna 312at the depth of the spine, thereby improving the quality of scannedimages for this region. The second antenna 312 augments the signal ofthe first antenna 302 as the distance from the top of the solenoidalcoils 314, 316 and 318 increases.

Solenoidal coil portions 314, 316 and 318 and latches 322 and 328 forman integral detachable unit. As depicted, latches 322 and 324 andlatches 328 and 330 form male-female pairs that divide the antenna 300into a front section comprising latches 322 and 328 and solenoidal coilportions 314, 316 and 318 and a bottom section comprising first antenna302, latch members 324 and 330, locking knobs 340 and 342, andsolenoidal coil portions 344, 346 and 348. As such, the quadratureantenna 300 opens in the front by removal of the front section from theback section. Detachable front and bottom sections allow forinterchangeable varying size front sections that can optimize the coilsize to the patient. In addition, the exposed portion of the solenoidalcoil, including the removable front section, comprises a grid-like orskeletonized structure, which results in weight reduction and minimizesclaustrophobic patient responses. The front section of quadratureantenna 300 may be optionally left off to allow the first or planarantenna 302 to function as a stand-alone unit.

The quadrature antenna 302 incorporates positioning features that allowthe user to attach the coil assembly to the bed 24 of FIGS. 1 and 2 andto vertically adjust the assembly along the bed to accommodate thepatient's anatomy. In addition, the positioning features allow anoperator to easily lock the coil assembly in place anywhere along thevertical axis of the bed and use the coil with the patient sitting,standing, recumbent or at any angle. Methods and structures forattaching, adjusting and locking an antenna to the bed are disclosed inthe '843 application; the same methods and structures can be used toattach, adjust and lock any of the antenna assemblies or arrangementswhich are described herein.

In a method in accordance with a further aspect of the invention, thequadrature antenna 300 is attached to the patient support 24. A patientP is then disposed on the patient support such that the posteriorsurface of the patient's torso is closely juxtaposed to the patientsupport and with first antenna 302. In this way the patient's spine isadjacent to the first antenna 302. The front section of the antenna 300is then latched into place. As such, the coil vector V_(C302) of thefirst antenna 302 is perpendicular to the static magnetic field vectorB₀ and to the support surface 26. The coil vector V_(C312) of the secondantenna 312 project in a direction parallel to lengthwise axis 25 whilebeing perpendicular to static magnetic field vector B₀. Both antennasare thereby available to receive the magnetic resonance signals emittedfrom the atomic nuclei of the patient P.

In a further variant, the one or more coils 303 shown in FIG. 9 may bepreferably oriented as shown in FIG. 9A. That is, the windings on one ormore coils 303′ of the planar antenna 302′ of FIG. 9A comprise a phasedarray of two coupled overlapping loops. As shown, the overlap isoriented longitudinally along the patient's body, i.e., along the longaxis of the patient's body. In this way, the proximity of the coil to apatient's spinal cord is accomplished, resulting in improvedsignal-to-noise ratio in the area of interest.

Turning now to FIG. 10, which schematically illustrates anotherembodiment of a quadrature coil antenna 400 in accordance with thepresent invention. Quadrature coil antenna 400 comprises receivingsolenoidal coil antenna 404 which comprises coils 412 and 414.Solenoidal coil antenna 404 is combined in quadrature mode with a saddlecoil 424. One portion of saddle coil antenna 424 comprises the U-shapedcoil 426 and an arcuate run R₁ transverse to the U-shaped coil 426 alongmember 430 as shown. Another portion of saddle coil antenna 424 isformed by the U-shaped coil 428 and arcuate run R₂, which runstransverse to the U-shaped coil 428 along member 430. As shown, thesaddle coil 424 is rotated 90 degrees so that its magnetic sensitivityis now aligned posterior to anterior with respect to a patient'sanatomy. The coil vector V_(C424) of the saddle coil antenna 424projects in a direction perpendicular to static magnetic field vector B₀and to the coil vector V_(C404) of solenoidal coil antenna 404 when usedin the apparatus 1 of FIGS. 1 and 2. The coil vector V_(C404) of coilantenna 404 also projects in a direction substantially perpendicular tostatic magnetic field vector B₀.

The solenoidal antenna 404 is mounted onto a base 440. The U-shapedcoils of the saddle coil antenna 424 are integrated with the solenoidalantenna 404 to form a skeletal structure into which a patient's head maybe inserted. The antenna 400 may be attached to the patient bed 24 viathe base 440 and vertically adjusted along the bed to adjust thepatient's anatomy. The antenna may also be easily locked into placeanywhere along the vertical axis 25 of the bed 24. The attachment,vertical adjustment and locking features are described in the '843application. The saddle coil 424 enhances the sensitivity in thedirection of the static magnetic field vector (B₀ in FIGS. 1 and 2). Inaddition, the patient's line of sight remains unobstructed during a scanwhich reduces claustrophobic effects. The antenna 400 also includes aconvenient and effective left-right and front-back immobilization systemcomprising adjustable clamps 450, which is adjustable to the patient'sanatomy.

In a further variant, the coil 400 may be implemented so as to includeseparable portions or with a flip-up like visor. In such an embodiment,electrical continuity may be maintained by including male-female socketsat the separation points.

In accordance with an additional method aspect of the present invention,quadrature coil antenna 400 is attached to the patient support 24. Apatient P is then disposed on the patient support such that thepatient's head is placed in the quadrature coil antenna 400. Stabilizingclamps 450 may then be used to stabilize the patient's head. In thisposition, the coil vector V_(C404) of solenoidal coil antenna 404projects in a direction parallel to lengthwise axis 25 and perpendicularto static field vector B₀. Saddle coil vector V_(C424) projects in adirection transverse to the support surface 26 and is also perpendicularto static field vector B₀. The patient's head may then be scanned withthe patient support rotated or positioned in the many orientationsdiscussed hereinabove. In particular, the adjustable clamps 450 providestabilization with the patient rotated or titled in many positionspreviously discussed hereinabove in relation to FIGS. 1, 2 and 5.

Turning now to FIG. 11A, there is illustrated a schematic of yet anotherquadrature coil antenna in accordance with an aspect of the presentinvention. Quadrature coil 500 is used for preferably imaging apatient's knee. As can be best seen from FIG. 11B, quadrature coil 500comprises a solenoidal-receiver coil 504 and a saddle-style receivercoil 508. Solenoidal-coil receiver 504 comprises individual coils 504 ₁,504 ₂, 504 ₃ and 504 ₄. In particular, coils 504 ₄ and 504 ₃ form onesolenoidal loop and coils 504 ₁ and 504 ₂ form another solenoidal loop.This solenoidal coil vector V_(C504) projects in a directionperpendicular to static field vector B₀ when used in the apparatus 1 ofFIGS. 1 and 2. Saddle coil 508 comprises coil members 508 ₁, 508 ₂, 508₃ and 508 ₄. Coil members 508 ₁ and 508 ₂ form a continuous loopcomprising the upper portion of saddle coil 508. Saddle coil members 508₃ and 508 ₄ form another loop comprising the lower portion of saddlecoil receiver 508. A saddle-coil vector V_(C508) projects in a directionperpendicular to static-magnetic field V0 when used in the apparatus 1of FIGS. 1 and 2. As FIG. 11B shows, the windings of the solenoidalcoils 504 encircle the windings of the saddle coils 508.

In a first embodiment, knee-coil 500 may be implemented to open at latchmembers 518 and 520 (see FIG. 11A.) A patient's knee K is thenpositioned within knee-coil 500 and the antenna assembly is completed bylatching members 518 and 520. In accordance with this first embodimentof knee coil 500, electrical continuity can be maintained by includingmale-female members where solenoidal coils 504 ₁ through 504 ₄ need tobe mated. The patient is then placed on support surface 26. Supportsurface 26 or table 24 is then moved into position so that the patient'sknee is within the static-magnetic field. Imaging then proceeds. Inaccordance with the present invention, such imaging may proceed under aweight bearing or non-weight bearing condition.

In accordance with a further variant, knee coil 500 may be implementedas a single integrated unit, which is then pulled over a patient's footup to the patient's knee. In addition, the knee coil 500 may also beimplemented such that it swings open at either latch 518 or 520.

In addition to the magnet structure shown in FIGS. 1, 2 and 5, thequadrature coil arrangement described hereinabove may also be used in amagnet structure 1000, as shown in FIG. 12. The magnet 1000 includes astationary magnet having a pair of elements, 1010 and 1020, spaced apartfrom one another along horizontal axis X. A magnetic air gap betweenelements 1010 and 1020 define a patient-receiving space 1035. Each ofthe elements 1010 and 1020 include one or more solenoidalsuperconducting coils 1040. The coils 1040 are operative to directmagnetic flux between the elements 1010 and 1020 so as to establish ahorizontal static magnetic field B₀. The elements 1010 and 1020 aremounted to structural support member 1045, which maintains the gapbetween the elements. The magnet 1000 may optionally includeferromagnetic poles 1051. However, poles 1051 may be eliminated and themagnet 1000 may nonetheless operate in accordance with the presentinvention.

In accordance with the embodiment shown in FIG. 12, a patient P may bepositioned within the patient-receiving space 1035 such that the longaxis 1055 of the patient's body is transverse to static magnetic B₀. Thepatient may be positioned in the sitting or standing position inaccordance with the requirements associated with the medical procedure.In addition, the patient may also be fitted with any of the quadraturecoil antennas described in detail hereinabove so that magnetic resonancescanning may be advantageously performed. In particular, thesignal-to-noise ratios improvement of up to √{square root over (2)} maybe achieved in accordance with this embodiment.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims. Inparticular, quadrature coils may be designed for many more parts of thehuman anatomy, e.g., the ankle, wrist, shoulder, neck, foot, breast,etc., that would provide improved signal-to-noise ratio performance.

1. A system for magnetic resonance imaging, comprising: a magnetdefining a patient-receiving space and having a static magnetic fieldwith a field vector in a substantially horizontal direction; a patientsupport having a support surface for a human body, said patient supportbeing positioned within said patient-receiving space and being pivotableabout a horizontal pivot axis; a coil antenna arrangement for receivinga signal from a patient disposed within said receiving space, said coilantenna including a first antenna having a first coil vector and asecond antenna having a second coil vector, said first coil vector andsaid second coil vector being transverse to said static magnetic fieldvector, and wherein said static magnetic field vector is orientedsubstantially transverse to the long axis of a patient disposed withinsaid patient-receiving space; and wherein said first antenna comprises asolenoidal coil antenna including a top portion and a bottom portion,the top portion and the bottom portion of the solenoidal coil antennadetachably attached to each other, and wherein said second antennacomprises a saddle coil antenna and said first coil vector issubstantially transverse to said second coil vector.
 2. The system asclaimed in claim 1, wherein said bottom portion of the solenoidalantenna is mounted onto a base including a patient support having asupport surface for a human body.
 3. The system as claimed in claim 1,wherein said saddle shaped antenna further comprises at least twoU-shaped coils that are disposed above each other and integrated withsaid solenoidal antenna to form a skeletal frame.
 4. A system formagnetic resonance imaging, comprising: a magnet defining apatient-receiving space and having a static magnetic field with a fieldvector in a substantially horizontal direction; a patient support havinga support surface for a human body, said patient support beingpositioned within said patient-receiving space and being pivotable abouta horizontal pivot axis; a coil antenna arrangement for receiving asignal from a patient disposed within said receiving space, said coilantenna including a first antenna having a first coil vector and asecond antenna having a second coil vector, said first coil vector andsaid second coil vector being transverse to said static magnetic fieldvector, and wherein said static magnetic field vector is orientedsubstantially transverse to the long axis of a patient disposed withinsaid patient-receiving space; and wherein said first antenna comprises asolenoidal coil antenna including a top portion and a bottom portionmounted onto a base, the top portion and the bottom portion of thesolenoidal coil antenna detachably attached to each other, and whereinsaid second antenna comprises a saddle coil antenna.
 5. The antenna ofclaim 4, wherein said saddle shaped antenna further comprises at leasttwo U-shaped coils that are disposed above each other and integratedwith said solenoidal antenna to form a skeletal frame.
 6. The antenna ofclaim 5, wherein at least one of the U-shaped coils include a firstarcuate run transverse to said at least one U-shaped coil.
 7. Apparatusfor magnetic resonance imaging, comprising: a magnet defining apatient-receiving space and having a static magnetic field with a fieldvector in a substantially horizontal direction; a patient support havinga support surface for a human body, said patient support beingpositioned within said patient-receiving space and being pivotable abouta horizontal pivot axis; a coil antenna arrangement for receiving asignal from a patient disposed within said receiving space, said coilantenna including a solenoidal coil antenna having a first coil vectorand a saddle coil antenna having a second coil vector, said first coilvector and said second coil vector being transverse to a static magneticfield vector; and wherein said solenoidal coil antenna includes a topportion and a bottom portion, the top portion and the bottom portion ofsaid solenoidal coil antenna detachably attached to each other.
 8. Theapparatus as claimed in claim 7, wherein said bottom portion of saidsolenoidal antenna is mounted onto a base.
 9. The apparatus as claimedin claim 7, wherein the solenoidal coil antenna further comprises aplurality of coils arranged along an axis parallel to the first coilvector.
 10. The apparatus as claimed in claim 7, wherein said saddleshaped antenna further comprises at least two U-shaped coils that aredisposed above each other and integrated with said solenoidal antenna toform a skeletal frame.
 11. The apparatus as claimed in claim 10, whereinthe at least two U-Shaped coils are arranged parallel to the base. 12.The apparatus as claimed in claim 10, wherein the U-Shaped coils includea coil having a portion extending along an axis parallel to the secondcoil vector.
 13. The apparatus as claimed in claim 10, wherein the atleast two U-shaped coil and saddle coil intersect at a normal angle. 14.The apparatus as claimed in claim 10, wherein the at least two U-shapedcoils comprises two U-shaped coils such that the two U-shaped coils anda plurality of solenoidal coils form the frame to include a space forallowing a patient to see through.
 15. The apparatus as claimed in claim10, wherein the saddle coil antenna further includes an arcuate run thatis transverse to the U-shaped coils.
 16. The apparatus as claimed inclaim 15, wherein the arcuate run is parallel to the solenoidal coilantenna.